Marcus Derrickson averaged 15.9 points and 8.1 rebounds as a junior. (Jonathan Newton/The Washington Post)

Georgetown forward Marcus Derrickson announced Monday that he will enter the NBA draft and hire an agent after three seasons with the Hoyas. The junior from Bowie thanked Coach Patrick Ewing in an Instagram post announcing his decision.

The announcement was unexpected: The 6-foot-7 forward had said multiple times this past season that he planned on staying for his senior season.

Derrickson credited Ewing’s style of play for much of his success this past year; he was Georgetown’s second-leading scorer and rebounder behind junior center Jessie Govan. Derrickson averaged 15.9 points and 8.1 rebounds in 31.9 minutes per game and was the team’s most efficient three-point shooter, converting 46.5 percent of 101 attempts. He averaged a team-high 17.2 points in Big East Conference play.

Derrickson’s departure leaves the Hoyas with an important roster spot to fill. It also raises questions about Govan’s future at Georgetown: After the Hoyas lost to St. John’s in the first round of the Big East tournament in March, the center implied both he and Derrickson would return.

More basketball from The Post:

As high school star skips college for NBA’s G League, others remain skeptical

The playoffs are nearly here, and the Wizards are grappling with what they’ve become

Jerry Brewer: It’s Villanova’s world, and college basketball should be happy to be part of it